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<div class="titlepage"><div><div><h3 class="title">
<a name="fiber.integration.event_driven_program"></a><a class="link" href="event_driven_program.html" title="Event-Driven Program">Event-Driven
      Program</a>
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<p>
        Consider a classic event-driven program, organized around a main loop that
        fetches and dispatches incoming I/O events. You are introducing <span class="bold"><strong>Boost.Fiber</strong></span> because certain asynchronous I/O sequences
        are logically sequential, and for those you want to write and maintain code
        that looks and acts sequential.
      </p>
<p>
        You are launching fibers on the application&#8217;s main thread because certain
        of their actions will affect its user interface, and the application&#8217;s UI
        framework permits UI operations only on the main thread. Or perhaps those
        fibers need access to main-thread data, and it would be too expensive in
        runtime (or development time) to robustly defend every such data item with
        thread synchronization primitives.
      </p>
<p>
        You must ensure that the application&#8217;s main loop <span class="emphasis"><em>itself</em></span>
        doesn&#8217;t monopolize the processor: that the fibers it launches will get the
        CPU cycles they need.
      </p>
<p>
        The solution is the same as for any fiber that might claim the CPU for an
        extended time: introduce calls to <a class="link" href="../fiber_mgmt/this_fiber.html#this_fiber_yield"><code class="computeroutput">this_fiber::yield()</code></a>. The
        most straightforward approach is to call <code class="computeroutput"><span class="identifier">yield</span><span class="special">()</span></code> on every iteration of your existing main
        loop. In effect, this unifies the application&#8217;s main loop with <span class="bold"><strong>Boost.Fiber</strong></span>&#8217;s
        internal main loop. <code class="computeroutput"><span class="identifier">yield</span><span class="special">()</span></code> allows the fiber manager to run any fibers
        that have become ready since the previous iteration of the application&#8217;s main
        loop. When these fibers have had a turn, control passes to the thread&#8217;s main
        fiber, which returns from <code class="computeroutput"><span class="identifier">yield</span><span class="special">()</span></code> and resumes the application&#8217;s main loop.
      </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2013 Oliver Kowalke<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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